Unwanted sparks or arcs of electrical energy can present a problem. At a minimum, generation of sparks can interfere with light sensitive applications or ruin photosensitive emulsions. On another hand, of perhaps greatest concern is the generation of sparks in the presence of flammable or combustible materials, which can result in a fire or an explosion. It is for this latter reason that chemical producers, petroleum companies, and aerospace companies, just to name a few, study spark generation phenomena to prevent harms that might result from sparks or arcs caused by lightning, discharge of static electricity, or other sources.
To name one example, in the aerospace industry, it is a concern that lightning striking an aircraft could result in the generation of sparks where fuel-vapor mixtures might exist. The Federal Aviation Authority (FAA) recognizes that, at a minimum, spark energy of 200 uJ is capable of igniting a fuel-vapor mixture. As is understood in the art, although lightning strikes pass right through aluminum aircraft en route to a ground source and harm virtually never results, manufacturers remain vigilant in evaluating new materials and components to ensure unacceptable sparks are not produced. To that end, manufacturers test aircraft materials and components by simulating lightning strikes and monitoring to determine if sparks are produced.
Spark detection tests are conducted in light-sealed chambers. Simulated lightning is generated by discharging a bank of high voltage capacitors. The simulated lightning is applied to an object of study, such as a “coupon” of aircraft fuselage material, or joined sections of aircraft hull material, which is coupled to ground. Whether the electrical charge carried by the simulated lightning strike passes through to ground or results in generation of spurious sparks is conventionally monitored photographically. Photographs of the object of study are taken by 35 millimeter or Polaroid® cameras. The shutter of the camera is opened before the simulated lightning strike is applied and closed before the light-sealed chamber is opened to study the object under test. As is known, ASA 1000 35 millimeter film or ASA 3000 Polaroid® film will reveal the emission of a 200 uJ or greater spark. Studying the resulting photographs, therefore, allows researchers to determine if sparks resulted from simulated lightning strikes and, specifically, where on the object of study sparks originated.
Unfortunately, photographic methods do not provide information as detailed or refined as researchers would like. Because the response of photographic film to light is highly nonlinear, the intensity of sparks generated must be estimated from the brightness of the image of the spark or the cross-sectional area on the film spanned by the spark's image. Film also may not be able to perceive light in the infrared spectrum or even the deep red of the visual spectrum. Thus, events of possible concern could be missed. Also, film cannot indicate exactly when the spark actually was generated during the interval the shutter was open. Further, film cannot indicated how long the event lasted or whether multiple sparks that might appear on a photograph occurred simultaneously or at different times. Finally, particularly with 35 millimeter film, researchers also must wait while the film is developed to begin their studies.
In an attempt to improve on photographic techniques, photomultiplier tubes (PMTs) also have been used to monitor sparks. For example, PMTs allow for determining precisely when sparks are generated. Also, the output of a PMT can be used to measure intensity of sparks detected. However, although PMTs are very sensitive and can detect even single-photon events, they also have disadvantages. For example, because of the unpredictability of the output of the photomultiplying process, the output may not accurately represent intensity of sparks recorded. Also, PMTs are expensive to manufacture and are extremely fragile. In addition, PMTs are very sensitive to noise common in high energy environments such as lightning testing chambers. PMTs also must be kept away from light sources, receiving light signals through expensive fiber-optic lines.
Therefore, there is an unmet need in the art for a better way to measure emission of potential sparks and to more precisely determine the timing and intensity of sparks emitted. At the same time, it is desired to have a spark detector that is inexpensive, durable, and that yields quick results.